I have tried to reduce the trigger pull on my R & S pistol from its current 9lbs to a more manageable 4ish lb without any success to date. So in seeking advice I attach a rough sketch of the trigger parts: -
Hopefully the detail is fairly clear in its indication of the trigger action.
I have been advised to polish (reducing with care) the top of the trigger at point ‘2’ but, whilst this has produced a nice crisp let-off, it has done nothing discernible to reduce trigger pressure.
I am reluctant to polish ‘2’ any further, fearing that a point will eventually be reached at which it fails to engage with notch ‘2a’and lodges in the half-cock notch ‘6’ or fires.
The only other thing I can think of is to (carefully) increase the ‘at-rest’ bend on the mainspring between points ‘x’ and ‘y’ to reduce the pressure of the spring at ‘3’ on the hammer wheel ‘3a’.
All advice gratefully received.
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December 29, 2012, 12:52 PM
Personally I'd leave her at 4# and let shooting do the rest of the polishing. But if ya really really just gotta have a lighter pull bending the spring would be the option.
December 29, 2012, 01:18 PM
Single action Colt springs are typically lightened by thinning & tapering them on the sides, and then highly polishing them so tiny scratches from filing or grinding doesn't leave a stress riser for them to break.
However a lighter mainspring doesn't really change the trigger pull weight very much.
Are you sure the trigger sear tip #2 and full cock hammer notch #2A are at exact right angles with each other?
If not, the trigger has to further cock the hammer back against mainspring tension when it is pulled across the hammer notch.
Check it very carefully by watching or feeling the hammer as the trigger is released, and see if the hammer moves to the rear very slightly as the sear is disengaged.
If it does, the improper sear / hammer notch angle is making the trigger pull 9 pounds, not the strength of the mainspring.
December 30, 2012, 01:13 PM
Many thanks for the advice.
I posted on both The High Road and MLGB forums with similar helpful responses from both.
I hope you’ll bear with a couple of additional questions.
1. Reference has been made to thinning the mainspring – does this mean reducing the thickness, or the width. Reference to an earlier post on High Road refers to thinning by either ‘tapering to the top’ or by ‘the hourglass method’? (I had assumed this meant dressing the edges rather than the flats).
If either is a possibility which is most advantageous?
2. I had also assumed that polishing the top of the trigger was unlikely to make a big (e.g. a 5lb reduction) difference to trigger pressure but now suspect I might be wrong?:-
My engineering expertise is limited but referring to the previous ‘Trigger/hammer detail’ and responses am I correct in saying:-
i) Trigger pressure at ‘1’ is a combination of:
a) Force from the mainspring at ‘3’ acting down at ‘2a’ on trigger sear ‘2’
b) Force from the locking pawl spring acting up on the underside of the trigger horizontal leg
c) The force required to disengage the trigger sear ‘2’ from the notch ‘2a’. This is variable dependent upon the shape and surface finish of both notch and sear and can crudely be illustrated by:-
ii) Adjusting the pressure of the pawl spring is neither easy nor advisable and reducing the mainspring pressure is possible but secondary to properly shaping the sear engagement.
All of which suggests I should try sear engagement supplemented (reluctantly) by mainspring thinning.
If the foregoing is sensible any comments (in particular on sear and spring profiling) would be welcomed.
December 30, 2012, 01:38 PM
Again, unless the hammer is extremely hard to cock, I don't think you have a mainspring problem causing a 9 lb trigger pull.
Mainspring tapering is done to ease hammer thumb cocking, not reduce trigger pull.
Your second drawing showing the "Probably just right" is not probably.
It is just right.
Your "far too heavy" drawing is what I believe the problem most likely is.
That, or an excessively stiff trigger / bolt flat spring.
Take that spring clear out and try the trigger pull without it and see how much difference in pull weight it makes.
I doubt anyone makes a reduced power replacement bolt spring for a Rogers and Spencer?
But that would address that.
Perhaps you could modify a Colt or Uberti SAA bolt spring.